Multi-port gas injection system and reactor system including same

ABSTRACT

A gas injection system, a reactor system including the gas injection system, and methods of using the gas injection system and reactor system are disclosed. The gas injection system can be used in gas-phase reactor systems to independently monitor and control gas flow rates in a plurality of channels of a gas injection system coupled to a reaction chamber.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to gas-phase reactors andsystems. More particularly, the disclosure relates to gas injectionsystems for introducing gas to a reaction chamber, to reactors andreactor systems including a gas injection system, and to methods ofusing same.

BACKGROUND OF THE DISCLOSURE

Gas-phase reactors, such as chemical vapor deposition (CVD),plasma-enhanced CVD (PECVD), and atomic layer deposition (ALD) reactors,can be used for a variety of applications, including depositing andetching materials on a substrate surface. For example, gas-phasereactors can be used to deposit and/or etch layers on a substrate toform semiconductor devices, flat panel display devices, photovoltaicdevices, microelectromechanical systems (MEMS), and the like.

A typical gas-phase reactor system includes a reactor including areaction chamber, one or more precursor and/or reactant gas sourcesfluidly coupled to the reaction chamber, one or more carrier and/orpurge gas sources fluidly coupled to the reaction chamber, a gasinjection system to deliver gases (e.g., precursor/reactant gas(es)and/or carrier/purge gas(es)) to the reaction chamber, and an exhaustsource fluidly coupled to the reaction chamber.

Generally, it is desirable to have uniform film properties (e.g., filmthickness and resistivity) across a surface of a substrate and/or tohave control over any desired variation. Various gas injection systemshave been developed to attempt to achieve uniform or controllable filmproperties. For example, gas injection systems including multiple portsor nozzles located within or adjacent the reaction chamber have beendeveloped to increase uniformity of film properties across a substratesurface. In such examples, a flow rate of gas to each port can beadjusted—e.g., manually, using a needle valve. Although this techniqueworks well for some applications, such systems may not be able toaccurately monitor and control gas flow to adequately address desireduniformity and/or controllability of film properties, particularly at ornear an edge of a substrate. Additionally, use of the needle valve maygenerate undesired particles—e.g., due to mechanical abrasion of valvecomponents.

As sizes of features formed on a substrate surface decrease, it becomesincreasingly important to control film properties, such as filmthickness and resistivity. Moreover, it may be desirable toindependently tune film properties; e.g., to independently tune filmthickness uniformity and/or resistivity in layers deposited usinggas-phase reactors, such as epitaxial layers grown using such reactors.Accordingly, improved gas injection systems, reactor systems includingan improved gas injection system, and methods of using the gas injectionand reactor systems are desired.

SUMMARY OF THE DISCLOSURE

Various embodiments of the present disclosure relate to gas injectionsystems, reactors and reactor systems including a gas injection system,and to methods of using the gas injection systems, reactors, and reactorsystems. While the ways in which various embodiments of the presentdisclosure address drawbacks of prior gas injection systems, reactors,and systems are discussed in more detail below, in general, variousembodiments of the disclosure provide gas injection systems that canprovide improved monitoring and control of gas (e.g., a mixture ofgases) flow rates to individual channels of a gas injection system,provide dynamic feedback of flow and/or flow ratios of gas to one ormore channels of a gas injection system, and/or provide improvedstability of flow rates and/or flow ratios of gas in each channel of agas injection system. Further, exemplary systems and methods allow finetuning of precursors and reactants provided to a reaction chamber and/ora substrate surface. In addition, exemplary gas injection systems canallow for independent tuning of film properties, such as film thickness,film thickness uniformity, film resistivity, composition profiles, andthe like. Exemplary gas injection systems can also be used to maintainpressure differentials at desired levels.

In accordance with exemplary embodiments of the disclosure, a gasinjection system includes a first gas supply line; a first gas manifoldcoupled to the first gas supply line, wherein the first gas manifoldcomprises a plurality of first gas outlets; a plurality of first massflow sensors, wherein at least one of the plurality of first gas flowsensors is coupled to each of the plurality of first gas outlets; aplurality of first gas valves, wherein at least one of the plurality offirst gas valves is coupled to an outlet of each of the plurality offirst gas flow sensors; and a controller (electrically) coupled to theplurality of first mass flow sensors and to the plurality of first gasvalves to control a desired flow ratio of a first gas through each of aplurality of first gas channels. Exemplary gas injection systems canalso include a second gas supply line; a second gas manifold coupled tothe second gas supply line, wherein the second gas manifold comprises aplurality of second gas outlets; a plurality of second gas flow sensors,wherein at least one of the plurality of second gas flow sensors iscoupled to each of the plurality of second gas outlets; a plurality ofsecond gas valves, wherein at least one of the plurality of second gasvalves is coupled to an outlet of each of the plurality of second gasflow sensors; and wherein a controller (e.g., the same controllercoupled to the plurality of first mass flow sensors and to the pluralityof first gas valves) is coupled to the plurality of second mass flowsensors and to the plurality of second gas valves to control a desiredflow ratio of a second gas through each of a plurality of second gaschannels. Gas injection systems in accordance with the presentdisclosure can similarly include three of more gas lines and thecorresponding components, as described in connection with the first andsecond gas lines and can use one or more controllers as describedherein. Use of the flow controllers as described herein can allowindependent control of gas flow rates to one or more channels (describedin more detail below) of a gas injection system, which, in turn, canallow for fine tuning of various properties of films deposited usingsuch systems and/or reactant/precursor concentration profiles within areaction chamber.

In accordance with additional exemplary embodiments of the disclosure, agas-phase reactor system includes one or more gas injection systems asdescribed herein. The exemplary systems can also include an exhaust(e.g., vacuum) source coupled to the reaction chamber, a first gassource fluidly coupled to the one or more first gas channels, and asecond gas source fluidly coupled to the one or more second gaschannels. Exemplary systems can also include additional gas (e.g.,dopant sources) and/or exhaust sources.

In accordance with yet additional exemplary embodiments of thedisclosure, a method of providing gas-phase reactants to a surface of asubstrate includes the steps of providing a gas-phase reactor system,providing a gas injection system as described herein, providing asubstrate within a reaction chamber of the reactor system, and exposingthe substrate to a first gas from the first gas source and a second gasfrom the second gas source. Exemplary methods can further includeautomatically adjusting one or more valves coupled to the one or morefirst gas channels and/or automatically adjusting one or more valvescoupled to the one or more second gas channels. Exemplary methods canalso include a step of providing an asymmetric setting of one or more ofa first gas from the first gas source and a second gas from the secondgas source—to, e.g., tune (e.g., independently) film properties, such asfilm thickness, film thickness uniformity, and film resistivity across asurface of a substrate, including an edge region of the substrate, andthe like.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

A more complete understanding of exemplary embodiments of the presentdisclosure can be derived by referring to the detailed description andclaims when considered in connection with the following illustrativefigures.

FIG. 1 illustrates a reactor system in accordance with at least oneexemplary embodiment of the present disclosure.

FIG. 2 schematically illustrates a gas injection system in accordancewith at least one exemplary embodiment of the disclosure.

FIG. 3 schematically illustrates another view of the gas injectionsystem in accordance with at least one exemplary embodiment of thedisclosure.

FIG. 4 schematically illustrates a portion of a control system inaccordance with at least one exemplary embodiment of the disclosure.

FIG. 5 schematically illustrates a control system in accordance with atleast one exemplary embodiment of the disclosure.

It will be appreciated that elements in the figures are illustrated forsimplicity and clarity and have not necessarily been drawn to scale. Forexample, the dimensions of some of the elements in the figures may beexaggerated relative to other elements to help to improve theunderstanding of illustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE DISCLOSURE

The description of exemplary embodiments provided below is merelyexemplary and is intended for purposes of illustration only; thefollowing description is not intended to limit the scope of thedisclosure or the claims. Moreover, recitation of multiple embodimentshaving stated features is not intended to exclude other embodimentshaving additional features or other embodiments incorporating differentcombinations of the stated features.

The present disclosure generally relates to gas injection systems, toreactors and reactor systems including a gas injection system, and tomethods of using the gas injection systems and systems. Gas injectionsystems, reactors, and reactor systems including a gas injection systemas described herein, can be used to process substrates, such assemiconductor wafers. By way of examples, the systems described hereincan be used to form or grow epitaxial layers (e.g., two component and/ordoped semiconductor layers) on a surface of a substrate. Exemplarysystems can be further used to provide etch chemistry to a substratesurface. For example, exemplary systems can provide a mixture of two ormore gases (e.g., collectively referred to herein as a mixture or simplygas or first gas) during a deposition (e.g., growth) process and/or twoor more gases (e.g., collectively referred to herein as a mixture orsimply gas or second gas) during an etch process. Both the depositionand etch gases can be used to grow an epitaxial film on a substrate.

As used herein, the terms “precursor” and/or “reactant” can refer to oneor more gases/vapors that take part in a chemical reaction or from whicha gas-phase substance that takes part in a reaction is derived. Thechemical reaction can take place in the gas phase and/or between a gasphase and a surface of a substrate and/or a species on a surface of asubstrate.

As used herein, a “substrate” refers to any material having a surfaceonto which material can be deposited. A substrate may include a bulkmaterial such as silicon (e.g., single crystal silicon) or may includeone or more layers overlying the bulk material. Further, the substratemay include various topologies, such as trenches, vias, lines, and thelike formed within or on at least a portion of a layer of the substrate.

As set forth in more detail below, use of exemplary gas injectionsystems as described herein is advantageous, because it allowsindependent metering and control of gas (e.g., a gas mixture) flowthrough various channels of the gas injection systems, and, in turn, toinput sites of a reaction chamber. The independent control of gas flowcan, in turn, allow independent tuning of film properties of films thatare formed using a reactor system including the gas injection system.For example, an exemplary gas injection system can be used toindependently tune resistivity and film thickness (or thicknessuniformity) of, for example, epitaxially formed layers on a substrate.Additionally or alternatively, exemplary gas injection systems can beused to compensate for gas flow variations, depletion rate variations,auto doping, or combinations thereof that may otherwise occur within areaction chamber of a reactor system. For example, the independent gasflow control at various input sites can be used to compensate for edgeeffects and/or a rotating substrate, which might otherwise causeundesired nonuniformity in one or more film properties. Further,exemplary gas injection systems can provide real-time feedback of gasflow in each channel. Exemplary gas injection systems are scalable toany desired number of channels and can be used with gas mixtures, whilemaintaining desired precision and control of flow rates (e.g.,independent of the makeup of the gas mixture). Additionally, exemplarygas injection systems of the present disclosure can be used forrelatively high gas flow rates (e.g., greater than five standard litersper minute of nitrogen through each channel) and/or can operate atrelatively high (e.g., near atmospheric) pressures, if desired. Theseand other features of the systems and methods described herein can beparticularly useful in depositing high-quality epitaxial layers onsubstrates.

Turning now to the figures, FIG. 1 illustrates an exemplary reactorsystem 100. Reactor system 100 can be used for a variety ofapplications, such as, for example, chemical vapor deposition (CVD),plasma-enhanced CVD (PECVD), atomic layer deposition (ALD), cleanprocesses, etch processes, and the like. Although exemplary embodimentsare described below in connection with epitaxial reactor systems, theembodiments and the invention are not so limited, unless statedotherwise.

In the illustrated example, reactor system 100 includes an optionalsubstrate handling system 102, a reaction chamber 104, a gas injectionsystem 106, and optionally a wall 108 disposed between reaction chamber104 and substrate handling system 102. System 100 can also include afirst gas source 112, a second gas source 114, and an exhaust source110. Although illustrated with two gas sources 112, 114, reactor system100 can include any suitable number of gas sources. Gas sources 112, 114can include, for example, a precursor gas, such as trichlorosilane,dichlorosilane, silane, disilane, and trisilane; a dopant source, suchas a gas comprising As, P, C, Ge, and B; and mixtures of gases,including mixtures of gases with a carrier gas, such as hydrogen,nitrogen, argon, helium or the like. Additionally or alternatively, oneof first gas source 112 and second gas source 114 can include anetchant, such as a chlorine-containing gas, such as hydrogen chloride.By way of examples, first gas source 112 and/or second gas source 114comprise a mixture of gases. Reactor system 100 can include any suitablenumber of reaction chambers 104 and substrate handling systems 102. Byway of example, reaction chamber 104 of reactor system 100 includes across flow, cold wall epitaxial reaction chamber. An exemplary reactorsystem including a horizontal cross flow reactor is available as asystem from ASM (e.g., the ASM Intrepid® reactor system).

During operation of reactor system 100, substrates, such assemiconductor wafers, (not illustrated) are transferred from, e.g.,substrate handling system 102, to reaction chamber 104. Oncesubstrate(s) are transferred to reaction chamber 104, one or more gasesfrom gas sources 112, 114, such as precursors, dopants, carrier gases,and/or purge gases are introduced into reaction chamber 104 via gasinjection system 106. As set forth in more detail below, gas injectionsystem 106 can be used to meter and control gas flow of one or moregases from first gas source 112 and second gas source 114 duringsubstrate processing and to provide desired flows of such gas(es) tomultiple sites within reaction chamber 104.

FIGS. 2 and 3 schematically illustrate a gas injection system 200,suitable for use as gas injection system 106, in accordance withexemplary embodiments of the disclosure. Gas injection system 200includes a first gas supply line 202 coupled to a first gas source 203,which can be the same or similar to gas source 112, and a second gassupply line 204 coupled to a second gas source 205, which can be thesame or similar to gas source 114. When referring to gas lines and fluidcomponents of gas injection system 200, the term “coupled” refers tofluidly coupled, and, unless stated otherwise, the lines or componentsneed not be directly fluidly coupled, but rather gas injection system200 could include other intervening elements, such as connectors,valves, meters, or the like.

With continued reference to FIGS. 2 and 3, gas injection system 200includes a first gas manifold 206 coupled to first gas supply line 202and a second gas manifold 208 coupled to second gas supply line 204.First gas manifold 206 includes a plurality of first gas outlets210-218. Similarly, second gas manifold 208 includes a plurality ofsecond gas outlets 220-228. First gas manifold 206 and second gasmanifold 208 are configured to receive gas from one or more gas lines(e.g., first and second gas lines 202, 204) and distribute the gas intoone or more channels, which are respectively defined, in part, by firstgas outlets 208-218 and second gas outlets 220-228. In the illustratedexample, each of the first and second gas streams from first gas source203 and second gas source 205 is divided into five gas channels.Although illustrated with five of each of first gas outlets 208-218 andsecond gas outlets 220-228, gas injection systems in accordance withthis disclosure can include any suitable number of first, second, and/orother gas outlets, corresponding to a number of channels for therespective gases. For example, exemplary systems can include, forexample, about 1-10 channels or include 5, 6, 7, 9, or more channels foreach gas. As illustrated, first gas manifold 206 and/or second gasmanifold 208 can include a loop configuration to facilitate even flowdistribution through the gas channels. In the illustrated examples,first gas channels and second gas channels are alternatingly adjacenteach other. However, this need not be the case.

As noted above, first gas source 203 and/or second gas source 205 can bea mixture of two or more gases. In such cases, one or more gases, whichmay, in turn, include a mixture of gases—or not, can be supplied fromother sources (not illustrated) to first gas source 203 and/or secondgas source 205 via flow controllers 207-213. When the source gasesupstream of flow controllers 207-213 are not mixtures of gases, flowcontrollers 207-209 can suitably be mass flow controllers.

Gas injection system 200 additionally includes a plurality of flowsensors 230-248 coupled to first and second gas outlets 210-228. In theillustrated example, each first and second gas outlets 210-228 iscoupled to a single flow sensor 230-248. However, in some cases, it maybe desirable to have some gas outlets that are not coupled to a flowsensor and/or to have some gas outlets that are coupled to more than oneflow sensor.

Flow sensors 230-248 can be used to monitor flow rates of gas mixturesand to provide real-time and/or historical flow rate information to auser for each channel—e.g., using a graphical user interface.Additionally or alternatively, flow sensors 230-248 can be coupled to acontroller (e.g., controller 302) and to gas valves 250-258 to providecontrolled flow ratio of the gases through gas valves 250-268. Byplacing at least one flow sensor 230-248 in each gas channel, the flowratio (e.g., relative flow rate) of gas through each channel can bemeasured and controlled, regardless of the gas composition. Exemplaryflow sensors 230-248 can be or include various flow sensors, e.g.,thermal mass flow sensors, pressure drop based flow sensors.

Gas valves 250-268 can include any suitable device to meter flow of agas. In accordance with various embodiments of the disclosure, gasvalves 250-258 each comprise proportional valves, such as solenoidvalves, pneumatic valves, or piezoelectric valves. A valve with arelatively high (e.g., 0.021-0.14) flow coefficient (Cv) may be selectedto reduce chocking downstream. As discussed in more detail below, gasvalves 250-268 may desirably operate under closed-loop control, but mayalso be capable (e.g., additionally) of operating under open-loopcontrol.

Flow sensors 230-248 and gas valves 250-268 can initially form part of,for example, a mass flow controller (e.g., an off-the-shelf mass flowcontroller), wherein the control function of the valve is replaced bycontroller 302. For example, flow meter 230 and gas valve 250 can formor be part of a mass flow controller 270 that is set to operate inopen-loop mode and wherein controller 302 provides closed-loop controlof valves 250-268. Flow sensors 232-248 and gas valves 252-258 cansimilarly form or be part of a mass flow controller 272-288. Thisconfiguration allows for implementation in standard reactorconfigurations and/or for use of readily-available mass flow controllersand flow sensors and valves.

Gas valves 250-268 can be coupled to a reaction chamber 290 via a flange292. Additional line (e.g., tubing) and suitable connectors can be usedto couple gas valves 250-268 to flange 292. Exemplary flange 292includes flange gas channels to maintain the channels until therespective gases exit into reaction chamber 290. An exemplary flangesuitable for use as flange 290 is disclosed in U.S. application Ser. No.14/218,690, filed Mar. 18, 2014, and entitled GAS INJECTION SYSTEM,REACTOR INCLUDING THE SYSTEM, AND METHODS OF USING THE SAME, thecontents of which are hereby incorporated herein by reference, to theextent such contents do not conflict with the present disclosure.

Gas injection system 200 can optionally include a moisture sample panel.A moisture sample panel can include, for example, one or more pressuretransducers, pneumatic valves, and/or restrictors. An exemplary moisturesample panel is disclosed in U.S. application Ser. No. 15/997,445, filedJun. 4, 2018, and entitled GAS DISTRIBUTION SYSTEM AND REACTOR SYSTEMINCLUDING SAME, the relevant contents of which are hereby incorporatedherein by reference, to the extent such contents do not conflict withthe present disclosure.

Reaction chamber 290 can be formed of, for example, quartz. Exemplaryoperating pressures within reaction chamber 290 during substrateprocessing can range from, for example, about 0.5 mTorr to about 780Torr. By way of examples, the pressure can range from about 2 mTorr toabout 780 Torr. In accordance with exemplary embodiments of thedisclosure, system 200 can provide desired, stable, independent flowcontrol within each channel over such pressure ranges.

Controller 302 can be configured to perform various functions and/orsteps as described herein. Controller 302 can include one or moremicroprocessors, memory elements, and/or switching elements to performthe various functions. Although illustrated as a single unit, controller302 can alternatively comprise multiple devices, as illustrated in FIG.5. By way of examples, controller 302 can be used to control flow of gasfrom first gas source 203 and/or second gas source 205 in a plurality ofgas channels. Controller 302 can be configured to provide open-loopand/or closed-loop flow control using, for example, the same hardware.In particular, controller 302 can be configured to provide desiredratios of a total flow of a respective gas (e.g., from first gas source203 or second gas source 205) in each of the channels coupled to therespective sources. In accordance with various examples of thedisclosure, controller 302 includes proportional-integral-derivative(PID) controllers, which allow independent, closed-loop control of thevarious controllable valves described herein, including gas valves250-268. With PID closed-loop control, system 200 can dynamically adjustflows in one or more (e.g., all) gas channels to set points and/orprovide stable, especially initial, flow rates of gases to reactionchamber 290 when switching between gas sources and/or when the operatingpressure is relatively high (e.g., near atmospheric pressure). Theclosed-loop control allows for automatic and stable control of flowrates through each channel over a wide variety of pressure ranges, suchas those set forth herein. The closed-loop control further allows forcontrol without tool matching, which is often required for traditionalsystems. By way of example, using PID control, an initial set point foreach controlled valve can be selected. Flow ratio feedback from anoutput of each flow sensor coupled to the controllable valve can then beused in connection with a PID controller of controller 302 to controlthe desired set point (i.e., flow ratio) of each of the controlledvalves.

FIG. 4 illustrates a portion of controller 302 for controlling a flowthrough a channel of gas injection system 200 using a typical mass flowcontroller, while overriding the control function of the mass flowcontroller. Initially, based on a flow ratio set point (e.g., from aprocess recipe) for each channel, controller 302 will first determinethe channel with highest flow ratio, and set its correlated controlvalve to a set point, typically below 100% open, such as 90% constantopen. Next, real-time nitrogen equivalent flow rate through each channelis measured using the respective flow meters. In the illustratedexample, the flow is measured by 5 flow meters as: Q1, Q2, Q3, Q4, Q5.Then the total flow rate is calculated by summing up the flow ratethrough each channel as: Q_(total)=Σ_(i=5) ⁵Q_(i). Actual flow ratiosthrough each channel are then calculated as:

${\alpha = \frac{Q_{1}}{Q_{total}}},{\beta = \frac{Q_{2}}{Q_{total}}},{\gamma = \frac{Q_{3}}{Q_{total}}},{\delta = \frac{Q_{4}}{Q_{total}}},{{\theta = \frac{Q_{5}}{Q_{total}}};}$

the actual ratios, as measure, can be displayed on a graphical userinterface. In addition to the channel with the highest flow ratio, therest of real time flow ratios are compared with their respective initialset points. An error function (E) is then calculated for each valve asthe difference between a flow ratio feedback and a flow ratio set point.The error function for each channel is used as PID input in controller302 for each channel/valve to be controlled. The PID output will be thecommand signal to control the respective valve in each channel.

FIG. 5 illustrates controller 302 in greater detail. In the illustratedexample, controller 302 includes a main controller 502 and aprogrammable logic controller (PLC) 504. Main controller 502 can be usedto send flow ratio set points to PLC 504 and to receive feedback fromPLC 504. In this configuration, main controller 502 acts as a mastercontroller and PLC controller 504 acts as a slave to main controller502. PLC controller 504 performs (e.g., using embedded firmware) the PIDand control functions described above in connection with FIG. 4. PLC 504can also be used to control valves 250-268 in an open-loopconfiguration—e.g., to allow fast-response, stable open-loop control.The communication between sensors 230-248, valves 250-268 (e.g., viacontrollers 270-288), PLC 504, and main controller 502 can be digitaland can be transmitted using suitable cables 506, 508.

Although exemplary embodiments of the present disclosure are set forthherein, it should be appreciated that the disclosure is not so limited.For example, although the gas injection and reactor systems aredescribed in connection with various specific configurations, thedisclosure is not necessarily limited to these examples. Variousmodifications, variations, and enhancements of the system and method setforth herein may be made without departing from the spirit and scope ofthe present disclosure.

The subject matter of the present disclosure includes all novel andnonobvious combinations and subcombinations of the various systems,components, and configurations, and other features, functions, acts,and/or properties disclosed herein, as well as any and all equivalentsthereof.

We claim:
 1. A gas injection system comprising: a first gas supply line;a first gas manifold coupled to the first gas supply line, wherein thefirst gas manifold comprises a plurality of first gas outlets; aplurality of first mass flow sensors, wherein at least one of theplurality of first gas flow sensors is coupled to each of the pluralityof first gas outlets; a plurality of first gas valves, wherein at leastone of the plurality of first gas valves is coupled to an outlet of eachof the plurality of first gas flow sensors; and a controller coupled tothe plurality of first mass flow sensors and to the plurality of firstgas valves to control a desired flow ratio of a first gas through eachof a plurality of first gas channels.
 2. The gas injection system ofclaim 1, wherein each of the plurality of first mass flow sensors isconfigured to measure relative flow of the first gas through each firstgas channel.
 3. The gas injection system of claim 1, wherein the firstgas comprises a mixture of gases.
 4. The gas injection system of claim1, further comprising: a second gas supply line; a second gas manifoldcoupled to the second gas supply line, wherein the second gas manifoldcomprises a plurality of second gas outlets; a plurality of second gasflow sensors, wherein at least one of the plurality of second gas flowsensors is coupled to each of the plurality of second gas outlets; and aplurality of second gas valves, wherein at least one of the plurality ofsecond gas valves is coupled to an outlet of each of the plurality ofsecond gas flow sensors; and wherein the controller is coupled to theplurality of second mass flow sensors and to the plurality of second gasvalves to control a desired flow ratio of a second gas through each of aplurality of second gas channels.
 5. The gas injection system of claim4, wherein each of the plurality of second mass flow sensors isconfigured to measure relative flow of the second gas through eachsecond gas channel.
 6. The gas injection system of claim 4, wherein thesecond gas comprises a mixture of gases.
 7. The gas injection system ofclaim 4, wherein the plurality of second gas valves comprises aproportional valve.
 8. The gas injection system of claim 4, wherein theplurality of second gas valves comprises a pneumatic valve.
 9. The gasinjection system of claim 4, further comprising a flange coupled to areaction chamber.
 10. The gas injection system of claim 9, wherein theplurality of first gas valves and the plurality of second gas valves arefluidly coupled to flange channels formed within the flange.
 11. The gasinjection system of claim 1, wherein the plurality of first gas valvescomprises a proportional valve.
 12. The gas injection system of claim 1,wherein the plurality of first gas valves comprises a pneumatic valve.13. The gas injection system of claim 1, further comprising a first massflow controller coupled to an inlet of the first gas supply line. 14.The gas injection system of claim 13, further comprising a second massflow controller coupled to the inlet of the first gas supply line.
 15. Areactor system comprising the gas injection system of claim
 1. 16. Thereactor system of claim 15, further comprising a reaction chambercoupled to the plurality of first gas valves.
 17. The reactor system ofclaim 16, further comprising a flange coupled to the reaction chamber,wherein the plurality of first gas valves are fluidly coupled to flangechannels formed within the flange.
 18. A reactor system comprising thegas injection system of claim
 4. 19. The reactor system of claim 18,further comprising a reaction chamber coupled to the plurality of secondgas valves.
 20. The reactor system of claim 18, further comprising avacuum source.